P0212: Injector Circuit/Open - Cylinder 12

Two things about P0212 are worth establishing before any testing, and neither is about injectors.

The first is that this code is the end of a sequence. SAE assigns one generic injector circuit code per cylinder from P0201 upward, and the block stops here at twelve. It stops because the next numbers were already spoken for: P0213 and P0214 belong to the cold start injectors, a different component doing a different job. So the sequence does not simply continue for engines with more cylinders. On a sixteen-cylinder engine there is no generic code for cylinder 13, and whatever the module reports for those cylinders comes out of the manufacturer's own numbering rather than the generic table. If P0212 appears on an engine with more than twelve cylinders, treat the cylinder number with suspicion and check the manufacturer's code list before assuming it means what it appears to mean.

The second is where cylinder 12 physically sits, because on this family the cylinder number is not just a label — it is a location, and location determines almost everything about what the repair costs. The convention nearly all twelve-cylinder engines follow is to number one bank first, front to back, then the other bank front to back: cylinders 1 to 6 on one side, 7 to 12 on the other. Under that scheme cylinder 12 is the rearmost cylinder on the second bank. On a longitudinally mounted V12 or W12 that puts it at the very back of the engine, tucked against the bulkhead, under whatever plenum, cowl trim and wiring channel the manufacturer routed across the back of the bay. Confirm the numbering diagram for your specific engine rather than taking this on trust, because a handful of designs number across the banks in pairs instead — but on the common convention, cylinder 12 is the one furthest from the front of the car.

That position produces three consequences a front-cylinder injector code does not carry. It is the far end of the injector harness branch for that bank, so its circuit passes through more of the loom and more intermediate routing than any of its neighbours before it reaches the module. It sits in the least ventilated part of the engine bay, where heat soaks after shutdown instead of being carried away, and heat-cycled connector housings and terminal seals at the back of a V12 age visibly faster than the ones at the front. And it lives directly below the scuttle and cowl area, which on an ageing car is where leaves collect, drains block, and water finds its way down onto the back of the engine — a corrosion route the front cylinders simply do not have. When a rear-cylinder injector circuit opens on a twenty-year-old V12, the connector and the last stretch of harness deserve suspicion before the injector does.

All of that changes the order of work rather than the principles. "Circuit/Open" describes an electrical state, not a failed part: a broken or chafed wire, a corroded or backed-out pin, a poor ground, a blown fuse in that bank's injector group, or an injector coil that has gone open will each produce it. But because this is the cylinder you least want to uncover twice, the discipline is to finish every test that can be done at the connector — feed voltage, coil resistance, a noid light to confirm the module is pulsing — before removing any part of the intake. Confirm what you are replacing while everything is still assembled.

Budget accordingly. An estimate written for "an injector" on one of these engines is usually priced from an average cylinder, and the rearmost one is not average — it commonly needs more of the plenum and rear wiring channel out of the way, which pushes the labour toward the top of the range rather than the middle. Ask specifically what the quote assumes about access. Note also that many twelve-cylinder engines split engine management across two control modules, one per bank, which changes how a whole-bank pattern of codes should be read; that argument is developed on the P0211 page and applies here unchanged.